In 2017, Mateo purchased a building that he used exclusively for business purposes, then he sold it in 2021 to an unrelated buyer. The value of the building was $12,000, excluding the land. He sold the building in December 2021 to a neighbor for $11,000. He is surprised that, even though he sold it at a loss, his return would show a gain. What is the best explanation for why Mateo had a gain?
